21720072 has 64 divisors (see below), whose sum is σ = 61300800. Its totient is φ = 6352640.

The previous prime is 21720053. The next prime is 21720109. The reversal of 21720072 is 27002712.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6238 + ... + 9074.

It is an arithmetic number, because the mean of its divisors is an integer number (957825).

Almost surely, 2^21720072 is an apocalyptic number.

21720072 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21720072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30650400).

21720072 is an abundant number, since it is smaller than the sum of its proper divisors (39580728).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21720072 is a wasteful number, since it uses less digits than its factorization.

21720072 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2886 (or 2882 counting only the distinct ones).

The product of its (nonzero) digits is 392, while the sum is 21.

The square root of 21720072 is about 4660.4798036254. The cubic root of 21720072 is about 279.0104182849.

Adding to 21720072 its reverse (27002712), we get a palindrome (48722784).

The spelling of 21720072 in words is "twenty-one million, seven hundred twenty thousand, seventy-two".